An automatic transmission comprising a gear type speed change mechanism having an automatic operation mode for automatically changing over a speed change ratio according to a throttle opening and a vehicle speed, and a manual operation mode wherein the speed change ratio is manually set by an operator, is disclosed for example in Tokkai Sho 60-256664 published by the Japanese Patent Office in 1985.
This transmission is provided with a mode change-over switch which changes over between an automatic operation mode and a manual operation mode, and an up switch and down switch used in the manual operation mode.
The operation of these switches is performed by a shift lever. In the manual operation mode, when the up switch is ON shift up is performed, and when the down switch is ON, shift down is performed.
However, when this manual operation mode is applied to a belt type continuously variable transmission, for example such as is indicated in Tokkai Hei 8-178055 published the Japanese Patent Office in 1996, or to a toroidal continuously variable transmission, the following problem occurs.
It is a characteristic of a continuously variable transmission wherein the speed change ratio is varied continuously, that compared to a conventional automatic transmission which varies the speed change ratio in a stepwise manner, a change of engine load due to a change of speed change ratio is smooth, and energy loss is small. However, when the manual operation mode is applied to a continuously variable transmission, and plural speed change ratios simulating a manual transmission are applied selectively, the engine output may temporarily fall considerably due for example to a shift-up operation.
Therefore in the manual operation mode, torque performance is less than for a continuous speed change operation in the automatic operation mode.
To resolve this problem, the number of speed change steps may be increased, but the frequency of speed change operations increases as a result.